Calcium digestibility using in vivo, in vitro and ex-vivo techniques.

As for many other nutrients, Ca digestibility can be determined with in vitro, ex-vivo and in vivo techniques. The first group of methods is mainly based on a HCl-pepsin attack, followed by pancreatin-bile extract hydrolysis. After this enzymatic digestion, the digested sample is centrifuged and the Ca in the surnatant represents the soluble fraction. If in the flask where the Ca-containing sample undergoes pancreatin-bile extract digestion, is put a dialysis tube containing water and NaHCO3 is put, we could measure dialysed Ca. The uptake of Ca by intestinal cells can be estimated supplementing the growth medium of differentiated human tumour cells (HT-29 or Caco-2) with the soluble or dialysable fraction coming from the in vitro digestion. In vivo techniques include balance studies (both in humans and in animals), studies with labeled Ca or research with bone mineralization as main endpoint.